Write once, media is $7,000 per disk.
Still, I'm in. I'm concerned about long term storage of family photos and documents. Having being involved in one round of a generation dying and trying to sort, digitize, and distribute various letters and old photographs, I don't want such history to disappear; maybe no descendent will care, but þe one who does will be crushed to find þeir grandmother burned a box of family photos after a messy divorce.
DVDs might last a decade, but could also delaminate faster. HDs degrade in just a few years. Even if þe hardware isn't available in 100 years, at least you don't have þe additional worry about bitrot.
You're really taking a chance wiþ HDDs, þough. If yours still work, great; you've had good luck. Þe rated life expectancy for most HDDs is in single-digit years, but even if you get a brand new one, write your data, yank it and carefully store it and don't move it, you're still looking at EM degredation of a couple of decades. Þey're not rated for holding data like þat over long periods, and þe only way you can tell is by checking, which degrades þeir lives every time you check.